crypto/rsa/rsa_pk1.c

   1 /*
   2  * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the OpenSSL license (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include "internal/constant_time_locl.h"
  11
  12 #include <stdio.h>
  13 #include "internal/cryptlib.h"
  14 #include <openssl/bn.h>
  15 #include <openssl/rsa.h>
  16 #include <openssl/rand.h>
  17
  18 int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
  19                                  const unsigned char *from, int flen)
  20 {
  21     int j;
  22     unsigned char *p;
  23
  24     if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
  25         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,
  26                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
  27         return 0;
  28     }
  29
  30     p = (unsigned char *)to;
  31
  32     *(p++) = 0;
  33     *(p++) = 1;                 /* Private Key BT (Block Type) */
  34
  35     /* pad out with 0xff data */
  36     j = tlen - 3 - flen;
  37     memset(p, 0xff, j);
  38     p += j;
  39     *(p++) = '\0';
  40     memcpy(p, from, (unsigned int)flen);
  41     return 1;
  42 }
  43
  44 int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
  45                                    const unsigned char *from, int flen,
  46                                    int num)
  47 {
  48     int i, j;
  49     const unsigned char *p;
  50
  51     p = from;
  52
  53     /*
  54      * The format is
  55      * 00 || 01 || PS || 00 || D
  56      * PS - padding string, at least 8 bytes of FF
  57      * D  - data.
  58      */
  59
  60     if (num < 11)
  61         return -1;
  62
  63     /* Accept inputs with and without the leading 0-byte. */
  64     if (num == flen) {
  65         if ((*p++) != 0x00) {
  66             RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
  67                    RSA_R_INVALID_PADDING);
  68             return -1;
  69         }
  70         flen--;
  71     }
  72
  73     if ((num != (flen + 1)) || (*(p++) != 0x01)) {
  74         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
  75                RSA_R_BLOCK_TYPE_IS_NOT_01);
  76         return -1;
  77     }
  78
  79     /* scan over padding data */
  80     j = flen - 1;               /* one for type. */
  81     for (i = 0; i < j; i++) {
  82         if (*p != 0xff) {       /* should decrypt to 0xff */
  83             if (*p == 0) {
  84                 p++;
  85                 break;
  86             } else {
  87                 RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
  88                        RSA_R_BAD_FIXED_HEADER_DECRYPT);
  89                 return -1;
  90             }
  91         }
  92         p++;
  93     }
  94
  95     if (i == j) {
  96         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
  97                RSA_R_NULL_BEFORE_BLOCK_MISSING);
  98         return -1;
  99     }
 100
 101     if (i < 8) {
 102         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
 103                RSA_R_BAD_PAD_BYTE_COUNT);
 104         return -1;
 105     }
 106     i++;                        /* Skip over the '\0' */
 107     j -= i;
 108     if (j > tlen) {
 109         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
 110         return -1;
 111     }
 112     memcpy(to, p, (unsigned int)j);
 113
 114     return j;
 115 }
 116
 117 int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
 118                                  const unsigned char *from, int flen)
 119 {
 120     int i, j;
 121     unsigned char *p;
 122
 123     if (flen > (tlen - 11)) {
 124         RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_2,
 125                RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
 126         return 0;
 127     }
 128
 129     p = (unsigned char *)to;
 130
 131     *(p++) = 0;
 132     *(p++) = 2;                 /* Public Key BT (Block Type) */
 133
 134     /* pad out with non-zero random data */
 135     j = tlen - 3 - flen;
 136
 137     if (RAND_bytes(p, j) <= 0)
 138         return 0;
 139     for (i = 0; i < j; i++) {
 140         if (*p == '\0')
 141             do {
 142                 if (RAND_bytes(p, 1) <= 0)
 143                     return 0;
 144             } while (*p == '\0');
 145         p++;
 146     }
 147
 148     *(p++) = '\0';
 149
 150     memcpy(p, from, (unsigned int)flen);
 151     return 1;
 152 }
 153
 154 int RSA_padding_check_PKCS1_type_2(unsigned char *to, int tlen,
 155                                    const unsigned char *from, int flen,
 156                                    int num)
 157 {
 158     int i;
 159     /* |em| is the encoded message, zero-padded to exactly |num| bytes */
 160     unsigned char *em = NULL;
 161     unsigned int good, found_zero_byte;
 162     int zero_index = 0, msg_index, mlen = -1;
 163
 164     if (tlen < 0 || flen < 0)
 165         return -1;
 166
 167     /*
 168      * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
 169      * section 7.2.2.
 170      */
 171
 172     if (flen > num)
 173         goto err;
 174
 175     if (num < 11)
 176         goto err;
 177
 178     if (flen != num) {
 179         em = OPENSSL_zalloc(num);
 180         if (em == NULL) {
 181             RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
 182             return -1;
 183         }
 184         /*
 185          * Caller is encouraged to pass zero-padded message created with
 186          * BN_bn2binpad, but if it doesn't, we do this zero-padding copy
 187          * to avoid leaking that information. The copy still leaks some
 188          * side-channel information, but it's impossible to have a fixed
 189          * memory access pattern since we can't read out of the bounds of
 190          * |from|.
 191          */
 192         memcpy(em + num - flen, from, flen);
 193         from = em;
 194     }
 195
 196     good = constant_time_is_zero(from[0]);
 197     good &= constant_time_eq(from[1], 2);
 198
 199     found_zero_byte = 0;
 200     for (i = 2; i < num; i++) {
 201         unsigned int equals0 = constant_time_is_zero(from[i]);
 202         zero_index =
 203             constant_time_select_int(~found_zero_byte & equals0, i,
 204                                      zero_index);
 205         found_zero_byte |= equals0;
 206     }
 207
 208     /*
 209      * PS must be at least 8 bytes long, and it starts two bytes into |from|.
 210      * If we never found a 0-byte, then |zero_index| is 0 and the check
 211      * also fails.
 212      */
 213     good &= constant_time_ge((unsigned int)(zero_index), 2 + 8);
 214
 215     /*
 216      * Skip the zero byte. This is incorrect if we never found a zero-byte
 217      * but in this case we also do not copy the message out.
 218      */
 219     msg_index = zero_index + 1;
 220     mlen = num - msg_index;
 221
 222     /*
 223      * For good measure, do this check in constant time as well; it could
 224      * leak something if |tlen| was assuming valid padding.
 225      */
 226     good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen));
 227
 228     /*
 229      * We can't continue in constant-time because we need to copy the result
 230      * and we cannot fake its length. This unavoidably leaks timing
 231      * information at the API boundary.
 232      */
 233     if (!good) {
 234         mlen = -1;
 235         goto err;
 236     }
 237
 238     memcpy(to, from + msg_index, mlen);
 239
 240  err:
 241     OPENSSL_clear_free(em, num);
 242     if (mlen == -1)
 243         RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
 244                RSA_R_PKCS_DECODING_ERROR);
 245     return mlen;
 246 }